Graduation carrier of plastics material with a graduation structure and fresnel zone ring

ABSTRACT

A graduation carrier of plastics material with a graduation structure, particularly for a photoelectric position measuring device. The graduation structure is a specially prefabricated lamina which is integrated with the graduation carrier with positive engagement. The free surface of the graduation structure and the free surface of the graduation carrier are located in a plane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a graduation carrier of plastics material with a graduation structure, particularly for a photoelectric position measuring device.

2. Description of the Related Art

A position measuring device of the above-described type is used for measuring the relative position of two objects which are movable relative to each other, for example, two machine components of a machine tool for positioning a tool relative to a workpiece to be processed. For this process, one of the objects is connected to the graduation carrier whose graduation structure is scanned by a scanning unit connected to the other object.

U.S. Pat. No. 4,806,751 discloses an angle-measuring device with a circular graduation carrier of plastics material. The graduation carrier includes a hub and a graduation structure in the form of a metal disk with recesses which is glued with the center portion thereof to the hub. In the outer portion with the recesses, the graduation carrier and the metal disk are spaced apart from each other. This graduation carrier with the only coarse graduation structure is relatively complicated with respect to construction and manufacture.

SUMMARY OF THE INVENTION

It is, therefore, the primary object of the present invention to substantially simplify the construction and manufacture of a graduation carrier of plastics material with a graduation structure.

In accordance with the present invention, the graduation structure is a separately prefabricated lamina or sheet which is integrated on the graduation carrier with positive engagement.

The present invention provides the particular advantages that the integration with positive engagement of the graduation structure in the graduation carrier of plastics material substantially simplifies and, thus, makes less expensive the construction and the manufacture by means of a casting method or an injection molding method. The manufacture is particularly inexpensive when multiple-purpose casting molds are used. The optical characteristics (absorption, reflectiveness) of the graduation structure can be varied in many ways. Depending on the construction, graduation structures with a resolution to the submicron range can be obtained.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1a is a cross-sectional view of a first embodiment of the graduation carrier with a graduation structure according to the present invention;

FIG. 1b is a plan view of the graduation carrier with graduation structure of FIG. 1;

FIGS. 2a, 2b, and 2c show the manufacturing steps of a second embodiment of the graduation carrier with graduation structure;

FIGS. 3a, 3b, and 3c show the manufacturing steps of a third embodiment of the graduation carrier with graduation structure;

FIGS. 4a, 4b, and 4c show the manufacturing steps of a fourth embodiment of the graduation carrier with graduation structure; and

FIGS. 5a, 5b, and 5c show the manufacturing steps of a fifth embodiment of the graduation carrier with graduation structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1a of the drawing is a cross-sectional view of a first embodiment of a circular graduation carrier TT₁ of plastics material with a hollow hub N₁ which is integrally cast with the graduation carrier. In FIG. 1b, the graduation carrier is shown in a plan view. A graduation structure TS₁ in the form of a separately prefabricated lamina is integrated with positive engagement on the free surface OT₁ of the graduation carrier TT₁. The free surface OT₁ of the graduation TT₁ and the free surface OS₁ of the graduation structure TS₁ are located in a plane. The graduation structure TS₁ has an incremental or absolute graduation T₁ which, in the conventional manner, is composed of light-permeable graduation lines and light-impermeable graduation lines.

The graduation carrier TT₁ with the graduation structure TS₁ is used, for example, in a photoelectric angle-measuring device for measuring the relative position of two objects which are movable relative to each other, for example, a carriage relative to the bed of a processing machine, not shown. For this purpose, the hollow hub N₁ of the graduation carrier TT₁ is connected to an adjusting spindle for the carriage and a scanning unit, not shown, of the angle-measuring device connected to the head scans the incremental or absolute graduation T₁ either in transmitted light or in incident light in order to obtain measurement values for the relative positions of the two objects. On the surface of the transparent graduation carrier TT₁ opposite the incremental graduation T₁, an optically effective structure, for example, in the form of a Fresnel zone ring F, may be provided. In addition to the hub N₁ and the Fresnel zone ring F, other functional elements provided are a toothing ZN on the hub N₁ and a toothing ZP on the periphery of the graduation carrier TT₁.

FIG. 2 shows in sectional views from left to right the manufacturing steps of a second embodiment of the circular graduation carrier TT₂ of plastics material with a graduation structure TS₂. The graduation structure TS₂ shown on the left of FIG. 2 is an especially prefabricated lamina in the form of a shaped etched component. The graduation structure TS₂ has a center bore B₂ and, as shown in the middle of FIG. 2, is concentrically placed on a base plate G₂ of a casting mold GF₂ by means of a centering pin ZZ₂. Liquid transparent plastics material for die casting is supplied through a sprue bore A₂ in the cover D₂ of the casting mold GF₂. After the plastics material has hardened, the base plate G₂ is removed and the finished graduation carrier TT₂ of plastics material with the graduation structure TS₂ and an integrally cast hub N₂ are removed, as can be seen on the right in FIG. 2. The graduation structure TS₂ is now integrated in the graduation carrier TT₂ with positive engagement and positionally stable. The surface OS₂ of the graduation structure TS₂ and the surface OT₂ of the graduation carrier TT₂ are located in a plane.

FIG. 3 shows in sectional views from left to right the manufacturing steps of a third embodiment of the circular graduation carrier TT₃ of plastics material with a graduation structure TS₃. As shown on the left of FIG. 2, the graduation structure TS₃ which is especially prefabricated as a lamina in the form of a nickel galvanic member is placed on a steel sheet S₃. The graduation structure TT₃ is concentrically arranged on a base plate G₃ of a casting mold GF₃. Centering is effected outside of the casting mold GF₃ in a manner which is not illustrated. Liquid transparent plastics material for die casting is supplied through a sprue bore A₃ in the cover D₃ of the casting mold GF₃, as shown in the middle of FIG. 3. After the plastics material has hardened, the base plate G₃ is removed and the finished graduation carrier TT₃ of plastics material with the graduation structure TS₃ and an integrally cast hub N₃ are removed. Subsequently, as shown on the right in FIG. 3, the steel sheet S₃ is pulled off. The graduation structure TS₃ is now integrated in the graduation TT₃ with positive engagement and positionally stable. The surface OS₃ of the graduation structure TS₃ and the surface OT₃ of the graduation carrier TT₃ are located in a plane.

FIG. 4 shows in sectional views from left to right the manufacturing steps of a fourth embodiment of the circular graduation carrier TT₄ of plastics material with a graduation structure TS₄. The graduation structure TS₄ which is a lamina in the form of a gold galvanic member, is especially prefabricated and placed on a base plate G₄ of a casting mold GF₄, as shown on the left in FIG. 4. Subsequently, the base plate G₄ is fastened to the casting mold GF₄, so that the graduation structure TS₄ is in a concentric position. Liquid transparent plastics material for die casting is supplied through a sprue bore A₄ through the cover D₄ of the casting mold GF₄, as illustrated in the middle of FIG. 4. After the plastics material has hardened, the base plate G₄ and the finished graduation TT₄ of plastics material with the graduation structure TS₄ and an integrally cast hub N₄ is pulled off from the base plate G₄, as can be seen on the right in FIG. 4. The graduation structure TS₄ is now integrated in the graduation carrier TT₄ with positive engagement and positionally stable. The surface OS₄ of the graduation structure TS₄ and the surface OT₄ of the graduation carrier TT₄ are located in a plane.

FIG. 5 shows in sectional views from left to right the manufacturing steps of a fifth embodiment of the graduation carrier TT₅ of plastics material with a graduation structure TS₅. In this embodiment, the graduation carrier TT₅ is rod-shaped. As shown on the left in FIG. 5, a graduation structure TS₅ with a graduation T₅ is especially prefabricated as a lamina and mounted on a steel sheet S₅. As shown in the middle of FIG. 5, a hardenable plastics material layer KS₅ is applied on a surface of the prefabricated graduation carrier TT₅ of plastics material. The graduation structure TS₅ is placed on the graduation carrier TT₅. As shown on the right in FIG. 5, after the plastics material layer KS₅ has hardened in a die casting mold, not shown, the steel sheet S₅ is pulled off. The graduation structure TS₅ with a graduation T₅ is now integrated in the graduation carrier TT₅ with positive engagement and positionally stable. The surface OS₅ of the graduation structure TS.sub. 5 and the surface OT₅ of the graduation carrier TT₅ are located in a plane. After hardening, a boundary surface no longer exists between the plastics material KS₅ and the graduation carrier TT₅. This rod-shaped graduation carrier TT₅ with the graduation structure TS₅ is used in a length-measuring device, not shown.

The graduation structure TS₁ may also be a stamped metal part or a member which is perforated by melting by means of a laser ray.

While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles. 

I claim:
 1. In a graduation carrier of plastic material with a graduation structure, particularly for a photoelectric position-measuring device, the improvement comprising the graduation structure being an especially prefabricated lamina which is integrated on the graduation carrier with positive engagement, the graduation structure and the graduation carrier having free surfaces, the free surfaces of the graduation structure and of the graduation carrier being located in a plane, a hub being integrally cast to the graduation carrier, the graduation carrier being circular, the hub being provided with a toothing, the graduation carrier having a circular periphery, the graduation carrier further comprising a toothing on the periphery, wherein an optically effective structure is formed in the graduation carrier, and wherein the optically effective structure is a Fresnel zone ring. 